Hydrated lime

"This chemical is commonly used because it is cost effective in situations
of very high acidity and large water flow. Extensive mechanical mixing is required
because hydrated lime does not dissolve in water. It can be bought in bulk
as a powder and must be dispensed via a mixer/aerator that mixes it with the
AMD water. It is important to not use too much hydrated lime, because any excess
should not enter the next stage, a pond within which the metals will settle.
Safety goggles must be used when handling this chemical because it can cause
blindness."